1. Field of the Invention
The present invention relates to a method for producing a semiconductor integrated circuit device, especially to a method for producing a semiconductor integrated circuit device having multi-layered buried wiring.
2. Description of Related Art
A structure of buried wiring is formed in a manner that wiring material is buried in an aperture for wiring such as a wiring groove or connection hole formed in an insulating film by wiring formation technologies as called Damascene Technologies (Single-Damascene Technology and Dual-Damascene Technology).
Recently, an increase in integration of the semiconductor integrated circuit device has reduced a clearance between such buried wiring lines. This increases such parasitic capacitance to cause a signal delay. Therefore, it may be desired to reduce the parasitic capacitance between wirings.
In U.S. Pat. No. 6,159,845 (hereinafter, referred to as “Patent”), a technique to form an air-gap between buried wiring lines is disclosed. FIGS. 1A to 1E in this Patent illustrate a method for producing one layer having buried wiring in the order of process steps. The technique shown may be characterized by reduced parasitic capacitance between adjacent buried wiring lines, because an insulating film intervening between adjacent buried wiring lines includes an air-gap.
In the Patent, a method for fabricating multi-layered buried wiring having an air-gap structure is not explicitly stated. From considerations conducted by the present inventors, it has been found that when the multi-layered buried wiring is formed using the technique described in the Patent, there may be problems of an increase in resistance of a via portion due to a defectively buried metal in the via portion, or parasitic capacitance that cannot be reduced between adjacent buried wiring lines because of metal films formed in the air-gap. This is because, as shown in FIG. 2, misalignment during a typical photolithographic process between underlying buried wiring portions 65 (single Damascene wiring) and the via portions 66 in the overlying buried wiring portions 68 (dual Damascene wiring) brings the via portions 66 into contact with an air-gap 67 formed between the underlying buried wiring portions 65: this causes a metal intrusion 69 in the air-gap 67 or a defectively buried metal 70 in the via portion when metal film is formed in the overlying buried wiring portion 68 including the via portion 66.